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Comment: 03:22 - 03:58 (00:36)
Source: Annenberg/CPB Resources - Earth Revealed - 17. Sedimentary Rocks: The Key to Past Environments
Keywords: "Dee Trent", crust, "igneous rock", "metamorphic rock", "sedimentary rock", "Earth's surface", weathering, erosion, "rock composition", "mechanical weathering", "chemical weathering", mineral
Our transcription: Although 95 percent of the Earth's crust is made up of igneous or metamorphic rocks, the surface itself consists primarily of sedimentary material.
The composition of this sediment is controlled by two factors: weathering and erosion.
Weathering and erosion influence the composition of sedimentary rocks because, first of all, the mechanical weathering breaks the rocks up and places them in small pieces making them more easily eroded.
The chemical weathering chemically breaks down certain minerals in preference to others.
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